So, I saw and used a lighting grid for the first time last week. We were discussing some of the common DIY techniques for grids since they can be a little pricey, and the most common was of course straws from starbucks and the like. However, Rob mentioned his was partially DIY since the grid innards were pre-assembled but used for some other purpose normally.
I did a quick internet search and found these, and I thought I would share.
Honeycomb Airflow Straightener
Some of them are made specifically for photography work, but are cheaper since there is no framework/exterior to them. So, assembly would be required, but still cheaper than what I've seen.